This invention relates to the production of golf club shafts, and, more particularly, to an approach for trimming golf club shaft blanks to as to have a desired final length and final deformation characteristics.
A golf club includes a thin, elongated shaft and a head affixed to one end of the shaft. Golf club shafts are typically made of a metal such as steel or titanium, or a composite material. In use, the club is swung by the standing golfer through an arc so that the head impacts a golf ball at ground level.
The shaft must be of the correct length for comfortable use by the golfer, and clubs are therefore manufactured and sold according to shaft length. Additionally, it is known that the hitting characteristics of the golf club are determined in part by the longitudinal deformation properties of the club shaft. The flexibility of the shaft (within limits), significantly affects the velocity of the club head as it impacts the ball and the expected fight distance of the ball. However the more flexible shafts are more difficult to control during the swing and require a greater skill level of the golfer. Consequently, golf club shafts may be made in a range of flexibilities for each length, with the selection of flexibility made by the golfer according to skill level and the intended use of the club.
Shafts made of a composite material such as carbon fibers embedded in an epoxy matrix are prepared by collating plies of an uncured prepreg composite material onto a form or in mold, and subsequently consolidating and curing the layup. The shafts are generally of a desired configuration with approximately the designed properties. However, due to variations in the starting material and in the fabrication procedure, there is typically a variation in the longitudinal flexural properties in a group of shafts of up to about .+-.5 percent from the nominal value. This variation, while acceptable for some circumstances, is too large for premium-quality clubs, where the variation should be no more than about .+-.1-2 percent from the nominal value.
A number of processing modifications may be made to the production operation. In order to reduce the property variation of the final acceptable shafts from the nominal. For example, the starting material may be more stringently screened and selected, greater care may be taken in the fabrication processing, the finished shafts may be individually hand processed to adjust their properties, or the unusable shafts may be diverted or scrapped. All of these alternatives significantly increase the cost of the acceptable shafts that meet the property-variation limitation indicated above, which may be acceptable for custom shafts but are not acceptable for shafts intended for mass markets.
There is a need for an approach to fabricating golf club shafts which are of the correct length and also have longitudinal flexure properties very close to a nominal value. The present invention fulfills this need, and further provides related advantages.